Ecology: Populations and Ecological Relationships

Ecology: Populations and Ecological Relationships

What is Ecology?

• Ecology is the study of interactions between organisms and their environment.

• Focuses on how organisms interact and how these interactions create an ecosystem.

• Explains how living organisms affect each other and the world they live in.

• Everything is connected (related to evolution).

Levels of Organization

• Analogous to cellular levels of organization (cell, tissue, organ, etc.).

• Ecological levels:

  • Individual

  • Population

  • Community

  • Ecosystem

  • Biome

  • Biosphere

• Each level becomes increasingly complex.

Organism

• A single individual.

• Examples: you, a dog, a zebra.

• Characterized by use of energy and reproduction.

Population

• A group of organisms of the same species.

• They can interbreed and live in the same place at the same time.

• Example: Squirrels in Virginia are a different population from squirrels in California because they don't interbreed or live in the same place.

Community

• Composed of multiple interacting populations.

• Organisms compete for resources, energy, mates, and territory.

• Organisms can also cooperate.

• Ecological relationships often describe community interactions.

Ecosystem

• Includes all living things (biotic factors) and non-living things (abiotic factors) in an area.

• Biotic factors: living organisms in an environment.

• Abiotic factors: non-living parts of an environment (water, temperature, soil, sun, air).

• Ecosystems comprises both biotic and abiotic components.

• Dirt: not alive but contains microorganisms.

• Water: not alive but contains microorganisms

Biosphere

• The global ecosystem.

• There is only one biosphere, which is Earth.

• It combines all ecosystems.

Biomes

• All ecosystems with a similar climate.

• Not always close to each other.

• Don't always have the same communities.

• Examples:

  • Desert

  • Savanna

  • Tropical rainforest

  • Chaparral

  • Marine: high biodiversity.

  • Temperate deciduous forests: high biodiversity (like Shenandoah).

  • Savannas: mid biodiversity.

  • Temperate grasslands: mid biodiversity.

  • Tundra: low biodiversity.

  • Arctic area

  • Coniferous forests

  • Polar and high mountain ice

Population Dynamics

• The goal of all living things is to reproduce and expand their population.

• A population is a group of individuals of one species living in a geographic area.

• Terms to describe population health include geographic range, population density, and population growth.

Geographic Range

• Area where a population can be found.

• Example: The range of the balsam poplar.

• Larger range often indicates better health.

Population Density

• Number of individuals in a given area.

• Populations vary in density (e.g., 50 balsam trees per acre, 100 people per square mile).

• More (or less) density doesn't always mean healthier

Population Growth

• How quickly the population size changes over time.

• In an ideal world with infinite resources, the population would grow infinitely.

Linear vs. Exponential Growth

• Example: Comparing \$5/hour for 20 hours vs. 1¢ doubling each hour for 20 hours.

  • \$5 x 20 = \$100

  • 1¢ doubling reaches \$10,485

• Linear growth: \$5/hour.

• Exponential growth: 1¢ doubling.

• Populations grow exponentially when reproducing.

Exponential Growth (J-Curve)

• If there are no limitations, populations will always grow exponentially.

• When graphed, this results in a J curve.

Factors Affecting Population Growth

• Populations are affected by the same things individual organisms experience.

• Measurements of population growth:

  • Natality: Number of births.

  • Fecundity: Ability to reproduce.

  • Fertility: Number of offspring.

  • Mortality: Death rate.

  • Life expectancy: Predicted length of survival.

Limiting Factors

• Factors that limit population growth.

• Examples: predators, lack of food.

• Cause organisms to die off or expand their range.

• Affect carrying capacity.

• Abiotic and biotic factors can both act as limiting factors.

Types of Limiting Factors

• Density-dependent factors: change based on the number of organisms present.

  • Often biotic.

  • Examples: predation, competition, disease.

  • Disease is density-dependent because denser populations increase the likelihood of spread.

• Density-independent factors: affect populations regardless of the number of organisms.

  • Often abiotic.

  • Examples: temperature, storms, floods, drought.

Logistic Model of Growth and Carrying Capacity

• Populations grow exponentially until they hit limiting factors, leading to a logistic model.

• The population stabilizes at the carrying capacity (K).

• Carrying capacity: the number of organisms an environment can support long-term.

• $K$ is the notation for carrying capacity and it has some value.

• Carrying capacity changes based on limiting factors.

• Environments can only support populations with enough food, water, and resources.

• Each species and population has a unique carrying capacity.

Population Dynamics Near Carrying Capacity

• Populations often overshoot carrying capacity, leading to die-off and fluctuation before stabilizing.

• If unable to maintain at carrying capacity, the population may go extinct.

• Reading carrying capacity graphs allows prediction of population changes.

• Below carrying capacity: population increases (birth rates exceed death rates).

• Above carrying capacity: population decreases (death rates exceed birth rates).

• Increases and decreases get smaller, eventually stabilizing at carrying capacity (birth rate equals death rate).

Review

• Carrying capacity is determined by limiting factors.

• Limiting factors are things like space, water, and food.

• Above carrying capacity, the population decreases.

• Below carrying capacity, the population increases.